Device for monitoring breathing during sleep and ramped control of CPAP treatment

ABSTRACT

A CPAP apparatus including: a variable pressured air source and means to vary the air pressure delivered therefrom; a nose piece for sealed air communication with a patient&#39;s respiratory system; an air communication line from the air source to the nose piece; a sound transducer adapted to be in sound communication with the patient&#39;s respiratory system; and a feedback system controlling the output pressure of the air source in response to an output from the transducer so as to increase the output air pressure from said air source, in response to detection of sound indicative of snoring, in accordance with a predefined procedure. The sound transducer, in its most general form, comprises a pressure transducer which, in addition to detecting snoring sounds, can detect other respiratory parameters such as the rate of breathing, inhaled air flow volume, and inhaled air flow rate. Output air pressure from air source is increased in response to one or more of these parameters in accordance with a pre-defined procedure.

[0001] This is a continuation of U.S. application Ser. No. 09/365,643,filed on Aug. 2, 1999, pending, which is a continuation of U.S.application Ser. No. 08/934,176, filed on Sep. 19, 1997, now abandoned,which is a continuation of U.S. application Ser. No. 08/838,462, filedon Apr. 7, 1997, now abandoned, which is a continuation of U.S.application Ser. No. 08/654,742, filed on May 29, 1996, now abandoned,which is a continuation of U.S. application Ser. No. 08/385,742, filedon Feb. 8, 1995, now abandoned, which is a continuation of U.S.application Ser. No. 08/100,556, filed Jul. 30, 1993, now abandoned,which is a divisional of U.S. application Ser. No. 07/892,692, filedMay. 27, 1992, now U.S. Pat. No. 5,245,995, which is a continuation ofU.S. application Ser. No. 07/548,108, filed Jul. 5, 1990, now abandoned,which is a continuation-in-part of U.S. application Ser. No. 07/457,757filed Dec. 21, 1989, now abandoned, which was the National Stage forInternational Application No. PCT/AU88/00215, filed on Jun. 27, 1988.

BACKGROUND ART

[0002] The present invention relates to the diagnosis and treatment ofpartial or complete upper airway occlusion, a condition where the upperairway collapses, particularly under the reduced pressure generated byinhalation. This is most likely to happen during unconsciousness, sleepor anaesthesia.

[0003] A particular application of the present invention is to thediagnosis and/or treatment of snoring and sleep apnea. Sleep apnea ischaracterized by complete occlusion of the upper airway passage duringsleep while snoring is characterized by partial occlusion. Obstructivesleep apnea sufferers repeatedly choke on their tongue and soft palatethroughout an entire sleep period resulting in lowered arterial bloodoxygen levels and poor quality of sleep. It should be realized thatalthough the following specification discusses sleep apnea in detail,the present invention also applies to the diagnosis and treatment ofother forms of upper airway disorders.

[0004] Reference to international patent publication WO 82/03548 willshow that the application of continuous positive airway pressure (CPAP)has been used as a means of treating the occurrence of obstructive sleepapnea. The patient is connected to a positive pressure air supply bymeans of a nose mask or nasal prongs. The air supply breathed by thepatient, is at all times, at slightly greater than atmospheric pressure.For example, gauge pressures will typically be within the range of 2 cmto 25 cm. It has been found that the application of continuous positiveairway pressure provides what can be described as a “pneumatic splint”,supporting and stabilizing the upper airway and thus eliminating theoccurrence of upper airway occlusions. It is effective in eliminatingboth snoring and obstructive sleep apnea and in many cases, is effectivein treating central and mixed apnea.

[0005] The airway pressure required for effective CPAP therapy differsfrom patient to patient. In order to discover the airway pressure whichis most effective for a particular individual, the practice has been forthe patient to undergo two sleep studies at an appropriate observationfacility such as a hospital, clinic or laboratory. The first night isspent observing the patient in sleep and recording selected parameterssuch as oxygen saturation, chest wall and abdominal movement, air flow,expired CO₂, ECG, EEG, EMG and eye movement. This information can beinterpreted to diagnose the nature of the sleeping disorder and confirmthe presence or absence of apnea and where present, the frequency andduration of apneic episodes and extent and duration of associated oxygendesaturation. Apneas can be identified as obstructive, central or mixed.The second night is spent with the patient undergoing nasal CPAPtherapy. When apnea is observed the CPAP setting is increased to preventthe apnea. The pressure setting at the end of the sleep period, i.e.,the maximum used, is deemed to be the appropriate setting for thatpatient. For a given patient in a given physical condition there will befound different minimum pressures for various stages of sleep in orderto prevent occlusions. Furthermore, these various pressures will, infact, vary from day to day depending upon the patient's physicalcondition, for example, nasal congestion, general tiredness, effects ofdrugs such as alcohol, as well as their sleeping posture. Thus theappropriate pressure found in the laboratory is necessarily the maximumof all these minimum pressures for that particular night and is notnecessarily the ideal pressure for all occasions nor for every night. Itwill generally be higher than necessary for most of the night.

[0006] Also patients must be able to operate a CPAP system to deliverappropriate airway pressure at their home where their general physicalcondition or state of health may be quite different to that in the sleepclinic, and will certainly vary from day to day. The patient's physicalcondition often improves due to CPAP therapy. It is often the case thatafter a period of therapy the necessary airway pressure can be reducedby some amount while still preventing the occurrence of obstructivesleep apnea. However, the prior art provides no facility to takeadvantage of this fact other than by regular diagnostic sleep periods ina sleep clinic or hospital.

[0007] The long term effects of CPAP therapy are unknown so it isdesirable to keep the airway pressure as low as practicable,particularly if a patient requires long term treatment. Lower airwaypressures also result in a lower face mask pressure which is generallymore comfortable for the patient. It has been found that CPAP inducespatients to swallow and this inducement to swallow can be reduced bylowering the airway pressure. Thus it is desirable to use the lowestpracticable airway pressure that is effective in preventing airwayocclusion during CPAP therapy for the comfort and, possibly, the longterm safety of the patient. Also, a lower airway pressure requires lessenergy consumption and a less complex and therefore less expensiveapparatus which is generally quieter.

[0008] Low airway pressures are also desirable before and during theearly stage of each sleep period as the increased comfort of aninitially lower airway pressure allows the patient to more easily fallasleep. When a patient undergoing CPAP opens his mouth with pressurizedair being forced through the nose the pressured air exits out of themouth producing an unpleasant sensation. This can occur when the patientputs on the mask connected to the pressured air supply before fallingasleep and some patients will therefore leave the mask off for as longas possible and may in fact fall asleep without wearing the mask andtherefore without the benefits of the CPAP therapy.

[0009] Presently available CPAP units do not address this problem and sothere is a need to provide a CPAP device which will be more acceptableto the patient before and during initial sleep by operating at aninitially low pressure but automatically increasing to an appropriatetherapeutic pressure before apnea occurs.

[0010] In addition to the problems associated with administering CPAPtherapy there exists the inconvenience and cost of diagnosis which iscurrently undertaken by overnight observation at a sleep clinic or thelike. Hence a simple means whereby a patient's apnea problem can bediagnosed at home without supervision is clearly desirable as well as aCPAP device which will deliver a continuously minimum appropriatepressure for substantially the entire period of therapy.

[0011] Devices are available to detect apnea. For example, InternationalPatent publication WO/86/05965 discloses an apparatus which includesacoustic respiration sensors, background sound sensors and movementsensors. Such apparatus are capable of detecting breathing sounds,comparing those sounds with body movements and background noises and byfurther comparing the results with a data base of information, toindicate whether the patient is undergoing a normal or abnormalbreathing pattern. Such apparatus can sound an alarm on the occurrenceof apnea.

[0012] Another device which could be readily adapted to detect andrecord the occurrence of apneic episodes is disclosed in U.S. Pat. No.4,537,190. That apparatus is responsive to the CO₂ levels in exhaled airduring respiration and is also responsive to the absence of respiration(i.e., apnea) in which case it can switch on a ventilator.

[0013] These devices are deficient in that they do not take advantage ofthe indication of apnea obtained exclusively from a recording from asingle sound transducer (microphone) preferably located in the CPAP nosemask or prongs that can be interpreted by a skilled physician. The soundtransducer, in its most general form, consists of a pressure transducerwhich, in addition to detecting snoring sounds, can detect otherrespiratory parameters such as the rate of breathing, inhaled air flowor inhaled air flow rate. The inherent simplicity of this form ofmeasurement makes it safe and practicable for anybody to use in theirown home with a minimum of prior instruction.

[0014] Although diagnosis in a sleep clinic as outlined above isbeneficial, it has some deficiencies. A patient is likely not to sleepin a fully relaxed state in an unfamiliar environment and a single nightis insufficient to obtain a pressure setting that will be optimal in thelong run. Thus home therapy at the pressure setting arrived at in thisway is likely to be less than 100% effective on some occasions andhigher than necessary for a substantial portion of the time. The costand inconvenience of a sleep study in a hospital setting are to beavoided if possible.

[0015] A skilled physician can usually recognize the symptoms of sleepapnea from questioning and examining a patient. Where no otherindications are present there is very little risk in attempting nasalCPAP therapy without further testing as the treatment is fail safe andnon-invasive. However, a very useful intermediate step would be toanalyze the pattern of respiratory sounds over one or more full nightsof sleep. Interpretation of these patterns together with questioning andexamination will, in many cases, provide sufficient confirmation ofapnea to prescribe nasal CPAP therapy. If nasal CPAP eliminates thesymptoms of day time sleepiness (as assessed by the patient) and ofapneic snoring patterns (as assessed by analysis of recorded respiratorysounds while on nasal CPAP), the treatment can be continued. Furthercheck ups can be conducted at intervals recommended by the physician.

[0016] In the most general form of the device, the intermediate stepbefore attempting nasal CPAP therapy would be to analyze the patterns ofthe respiratory parameters that can be obtained from a single pressuretransducer. These parameters include, in addition to acoustic rate ofbreathing, inhaled/exhaled air volume and inhaled/exhaled air flow rate,and provide comprehensive information for the physician to assess thepatient's condition. This additional information, coming from the samepressure transducer, is available at marginal additional cost to theacoustic recording and with no additional complexity in home use by thepatient.

[0017] The measurement of other parameters would provide furtherinformation to assist diagnoses and the acoustic and/or otherrespiratory recordings described above can readily be used inconjunction with other monitors such as ECG and/or pulse oximetry.Suitable monitors are available to measure both these parameters in thehome but with increased information comes much higher cost of equipmentand increase complexity in using the equipment. The correlation betweenreduced oxygen saturation and apnea is sufficiently well established toinfer oxygen desaturation from the confirmation of an apneic event.

[0018] Diagnoses which are not conclusive from examination and homemonitoring will continue to be confirmed from full sleep studies in aSleep Disorders Center.

[0019] Thus the prior art monitors and methods are deficient at least inthat the resulting therapy is not 100% effective at all times, it isdelivered at higher pressure than necessary for substantial periods, theequipment is expensive and has required diagnosis in specializedclinics.

DISCLOSURE OF INVENTION

[0020] The present inventors have recognized the detection of the noiseof snoring or more particularly snoring patterns as a reliable parameterfor detecting apneas as well as the imminent onset of apneic episodes.Characteristic snoring patterns can be associated with various sleepconditions including apnea and in fact in most (perhaps 95%) of sleepapnea sufferers, distinctive snoring patterns closely precede apneicepisodes as will be later discussed. Characteristic patterns of otherrespiratory parameters such as rate of breathing, inhaled/exhaled airvolume and inhaled/exhaled air flow rate, obtainable from the samepressure transducer as snoring patterns, can also be used for detectingapneas as well as the imminent onset of apneic episodes. Any oneparameter or combination of parameters may be used for detecting apneasor other breathing disorders, as well as the imminent onset of apneas orother breathing disorders.

[0021] A pressure transducer such as a microphone is a suitable detectorof these characteristic snoring sounds, and in particular the sounds ofsnoring patterns. Furthermore, the quality of the sounds monitored canbe enhanced by placing the microphone within an enclosure which is insound communication with a patient's respiratory system. By enclosingthe microphone, a physical noise barrier isolates the microphone fromexternal sounds. If the enclosure is in sound communication with thepatient's respiratory system the natural stethoscope effect of thepatient's respiratory system is thereby exploited. A further benefit ofsuch a device is that the microphone is not in direct contact with anypart of the patient's body. Thus, relative movement between themicrophone and the patient's body, which is a noise source as far asmonitoring is concerned, can be avoided.

[0022] Monitoring of a patient's snoring patterns alone can in manyinstances provide information indicative of his/her condition, whetherhe/she suffers mild, medium or extreme apneic episodes, how often theepisodes occur and therefore whether CPAP therapy will be beneficial. Asnoring monitor can accordingly be used at least as a preliminarydiagnostic tool with or without monitoring other physiologicalparameters to provide information on the frequency and severity ofsnoring, hypopnea and apnea in a patient. Its simplicity and inexpensivenature allows it to be used at home in the patient's usual environmentwithout the expense of a night in a sleep clinic. In some cases, e.g.,where unusual snoring patterns are encountered, the diagnosis of thedata from the snoring monitor will not be conclusive and the traditionalfull diagnosis in a sleep clinic will be required.

[0023] Thus, in one form of this invention there is provided adiagnostic device comprising a nose piece substantially fluidly sealableto the nasal air passages of a patient, a sound transducer in soundcommunication with the interior of the nose piece so as to be, when inuse, in sound communication with the respiratory system of the patientand to detect and produce a signal responsive to the sounds of patientsnoring, and recording equipment associated with the sound transducerfor recording information indicative of the signal.

[0024] In another form of the diagnostic device, there is provided anose piece substantially fluidly sealable to, or in sealed fluidcommunication with, the nasal air passages of a patient, a pressuretransducer in pressure communication with the interior of the nose pieceso as to be in pressure communication with the respiratory system of thepatient and to detect and produce a signal or signals responsive tosnoring and other respiratory parameters, such as rate of breathing,inhaled/exhaled air volume and inhaled/exhaled air flow rate, of thepatient, and recording equipment associated with the pressure transducerfor recording information indicative of one or more of the signals.

[0025] In one preferred embodiment of the diagnostic device, theintensity of the signal is recorded with respect to time. In anotherembodiment of the diagnostic device the microphone output is fed throughan amplifier or filter to differentiate normal breathing sounds fromthose indicative of snoring, and the intensities and time pattern of thedifferentiated sounds are recorded. Further, in a embodiment of thediagnostic device the frequency and duration of airway occlusions arecalculated by preprogrammed processing of the detected signal, theprocessed signal is recorded as a time chart or a table interpreted bythe physician.

[0026] In another embodiment of the diagnostic device, the pressuretransducer measures or detects a number of audio or low frequency wavesgenerated within the mask during breathing including a high frequencyaudio wave produced by the air flow into the mask and by the rotatingelements of the air source, a low frequency audio wave produced by theresonance of the airways or chest cavity during snoring, a very lowfrequency large amplitude wave corresponding to the pressure variationsproduced by the air flowing over a section of the nose piece, which mayinclude a flow restrictor to amplify the pressure drop. After suitableamplification, the output signal from the pressure transducer passesthrough filtering and conditioning circuits to separate the differentwaves of interest, including the low frequency audio wave describedabove and the very low frequency pressure wave produced by the airflowing over the said section of the nose piece.

[0027] The breathing rate of interruption of breathing, the air flowrate during inhalation/exhalation and the beginning/end points of thebreathing cycle are derived from the very low frequency pressure waveafter further sampling or processing. Using a suitable integrationtechnique, the air flow is integrated for the duration of theinspiration and/or expiration phase using the said beginning/end points.The integral of air flow corresponds to the inhaled/exhaled air volumefor each breath. The processed signals are recorded as a time chart or atable interpreted by a physician.

[0028] Thus in a number of cases such a snoring monitor provides aneffective substitute for the traditional first night in the sleepclinic. The monitor in its more general form provides information onrespiratory parameters such as rate of breathing, inhaled/exhaled airvolume, and inhaled/exhaled air flow rate, as well as snoring. Wherediagnosis indicates CPAP therapy to be appropriate the patient can gostraight to the traditional second night at the sleep clinic so as todetermine their appropriate CPAP setting for their condition, or theycould commence use of an automatic CPAP device such as the unitdescribed hereunder.

[0029] The monitoring of snoring patterns is useful not only forrecording information regarding those patterns for diagnostic purposesbut is also useful in that certain snoring patterns are a precursor tomost apneic episodes in a large proportion of sleep apnea victims. Thus,an effective CPAP device can be controlled by a feedback system in whichsnoring patterns are monitored and CPAP pressure is raised at thedetection of predefined snoring patterns so as to provide increasedairway pressure before, and in fact generally prevent the occurrence of,apneic episodes.

[0030] Thus, in another form of the invention there is provided in aCPAP apparatus a feedback control comprising a sound monitoring devicein sound communication with the respiratory system of a patient whenusing the apparatus, and a processor responsive to output from the soundmonitoring device so as to control CPAP pressure according to patientrequirements as determined by output from the sound monitoring device inorder to prevent apneic episodes.

[0031] The monitoring of other respiratory parameters, as well assnoring, is also useful not only for recording those patterns fordiagnostic purposes but is also useful in that certain patterns of theseparameters are a precursor to most apneic episodes and other forms ofbreathing disorders that can be treated by nasal CPAP. Thus an effectiveCPAP device can be controlled by a feedback system in which patterns ofrespiratory parameters are monitored and CPAP pressure is raised at thedetection of pre-defined patterns so as to provide increased airwaypressure, before and in fact generally prevent the occurrence of apneicepisodes or other forms of breathing disorders.

[0032] For example, the air flow rate inhaled or exhaled by the patientis compared to a base line level for that patient and if the flow rateis lower than the base line, the CPAP pressure is raised. Alternatively,the time interval between the onset of each inspiration or expiration iscompared to a base line level for that patient and if the interval isgreater than the base line, the CPAP pressure is raised. Alternatively,the integrated inhaled or exhaled volume of air is averaged over arelatively large number of breaths to give a moving base line for thepatient. Simultaneously, the integrated inhaled or exhaled volume of airis averaged over a short time interval. If the volume over the shorttime interval is less than the volume over the relatively large numberof breaths by a specified amount, CPAP pressure is raised.

[0033] Preferably, the feedback control is cooperative with a variablespeed air compressor of the CPAP apparatus, the processor regulating thespeed of the compressor when in use by increasing speed in response to asaid signal equivalent to a preprogrammed signal indicative of apredetermined snoring pattern. The said signal could also be indicativeof a predetermined pattern in other respirator parameters.

[0034] Preferably, the control system furthermore decreases speed of theair compressor in the absence of the signal after a period of time inaccordance with the predefined procedure.

[0035] In another form of the feedback device of the invention there isprovided a CPAP apparatus including a variable speed air compressor, anose piece for sealed air communication with a patient's respiratorysystem, an air line from the compressor to the nose piece, an enclosedmicrophone connected to the air line so as to be in sound communicationwith the patient's respiratory system, and a feedback system controllingthe speed of the air compressor in response to an output from themicrophone so as to increase compressor speed in response to detectedsound indicative of heavy snoring in accordance with a pre-definedprocedure. Preferably, the feedback system reduces the speed of the aircompressor in response to an absence of the said sound in accordancewith the predefined procedure.

[0036] In another form of the apparatus there is provided a CPAPapparatus including a variable speed air compressor, a nose piece forsealed air communication with a patient's respiratory system, an airline from the compressor to the nose piece, a pressure transducerconnected to the air line so as to be in pressure communication with thepatient's respiratory system, and a feedback system controlling thespeed of the air compressor in response to an output or outputs from thepressure transducer so as to increase compressor speed in response todetected patterns of sound or respiratory parameters indicative ofsnoring or breathing disorders in accordance with a predefinedprocedure. Preferably the feedback system reduces the speed of the aircompressor in response to an absence of the said patterns of sound orrespiratory parameters in accordance with the predefined procedures.

[0037] Disadvantages in the prior art are also ameliorated by a furtheraspect of the invention which provides a variable speed air compressorand control system in the CPAP apparatus, the control system regulatingthe speed of the compressor when in sue by increasing its speed inaccordance with a predefined procedure whereby the commencement ofoperation of the compressor occurs at a preselected minimum speed with agradually increasing compressor speed over a preselected period of timeto a preselected maximum speed.

[0038] This embodiment of the invention provides an advantage in thatthe patient is exposed to a comfortably low pressure before fallingasleep and during initial stages of sleep while the necessarytherapeutic pressure is reached by the time it is required.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will now be described in detail by way ofreference to the attached drawings in which:

[0040]FIG. 1a is a schematic sectional view of one embodiment of asnoring detection apparatus in accordance with the present invention;

[0041]FIG. 1b is a schematic sectional view of another embodiment of asnoring detection apparatus in accordance with the present invention;

[0042]FIG. 2a is a slow recording of sound levels obtained using themonitor of the present invention for a patient suffering from sleepapnea;

[0043]FIG. 2b shows the correlation of sound patterns and blood oxygenlevels during a period of repetitive obstruction apnea;

[0044]FIG. 3 is a diagram of a further embodiment of the presentinvention;

[0045]FIG. 4 is a circuit diagram of the device of FIG. 3;

[0046]FIG. 5 is a diagram of an embodiment of another aspect of theinvention;

[0047]FIG. 6 is a circuit diagram of the device of FIG. 5;

[0048]FIG. 7 is a schematic sectional view of one embodiment of a moregeneral apparatus for detecting snoring and/or other respiratoryparameters in accordance with the present invention;

[0049]FIG. 8 shows the volume of air breathed by a patient in normalsleep contrasted with the declining volume breathed as the patientstarts to hypoventilate;

[0050]FIG. 9 shows the different pressure waves generated by theextraneous high frequency noise associated with air flow from the blowerand the pressure waves of interest indicative of snoring and breathingand the composite wave comprising the contribution of all sources ofpressure wave;

[0051]FIG. 10 shows how the composite wave from the pressure sensor isfiltered to generate information on the parameters of interest;

[0052]FIG. 11 shows in schematic form how any or all of these parameterscan be used either alone or by reference to control data to provide asignal to a Motor Speed Controller;

[0053]FIG. 12 shows in schematic form how the computing system whichanalyzes the parameters of interest with reference to control patientdata controls motor speed and air pressure delivered to the patient;and,

[0054]FIG. 13 shows an example of how the pressure wave generated bysnoring progressively increases; decreases the air pressure delivered tothe patient as directed by the computer system.

BEST MODE OF CARRYING OUT THE INVENTION

[0055]FIG. 1a illustrates a snoring detection device 10 comprising amicrophone 11, in sound communication with the container 12 of a nosemask. Air, being inhaled by the patient, enters the nasal passageways 14through the opening 13 in the nose mask 12 and is exhaled in the reversedirection. As the airway extends from the source of snoring soundswithin the patient's body, through the nasal passages 14 and out of theopening 13 in the nasal mask, the microphone 11 is ideally located totake advantage of the natural stethoscope formed by the enclosed airway.Hence the snoring and breathing sounds are focused and concentrated bythis arrangement. Alternatively, the microphone 11 may be locatedwithin, or attached externally of, a nasal prong device as illustratedin FIG. 1b. The detection device 10 can be used in a diagnostic deviceor a feedback control. In the case of the detection device 10 being usedin diagnostic equipment there is connected to the microphone 11 anelectronic processor/recorder which records signals from the microphone11 either on a time basis or after preprogrammed processing so as torecord for example tables of indexes such as the number of apneicepisodes, their duration, etc. The recorded data can then be reviewed bythe physician for diagnosis.

[0056]FIG. 2a shows a graph representing sound amplitudes recorded fromthe snoring detection device 10. The major calibration in the time scaledirection represents two minutes.

[0057] The effect of blower motor noise can be diminished or completelyremoved by setting a low gain on the recording device or passing thesignal through an amplitude filter to effectively ignore all soundsbelow a particular minimum amplitude or by passing the signals through alow pass frequency filter to effectively ignore sounds above its cut-offfrequency. An alternative method is to use a sound attenuator in the airline proximate the blower.

[0058] Part A of FIG. 2a is indicative of normal breathing, part Bindicates soft to moderate snoring, part C shows constant loud snoringand part E shows periods of silence punctuated by snoring. In section Dof the chart of FIG. 2a, it can be seen that the breathing soundintensity rises and falls. This is indicative of obstructive hypopnea, acondition in which the breath-by-breath intensity decreasesprogressively, and then increases. In this pattern the decreasingintensity of the snoring occurs when the upper airway is almost, but notentirely, sucked closed by strong inspiratory efforts. This pattern is a“pre-apneic” pattern.

[0059] The following part E, is therefore quickly interpreted by askilled physician as being indicative of sleep apnea, with periods ofairway occlusion which terminate with one or more loud breathing soundsfollowed by further occlusions.

[0060] The correlation between snoring patterns and arterial oxygen isshown in FIG. 2b. Clearly the snoring patterns are an accurate parameterfor detecting imminent apneic episodes, and more importantly periods oflow oxygen supply to the brain and other organs.

[0061] Thus recorded information derived from the signal of the device10 can be used for diagnostic purposes, such as initial diagnosis ofsleep apnea, without the need for the patient to stay overnight at anobservation facility. The sound patterns can be analyzed by a programmedmicroprocessor within the diagnostic unit so as to record tables ofindexes such as number of apneic episodes, their duration and time ofoccurrence. This is of economic significance because the cost of oneovernight observation is comparable to the purchase price of a CPAPdevice.

[0062] The nose prongs and mask 12 are convenient forms of containersfor the monitor device 10 however the container could take any otherconvenient form.

[0063] Furthermore, diagnostic apparatus in accordance with the presentinvention is suited for use by a patient with minimal supervision andtherefore may be used successfully at home, the recorded diagnosticinformation being conveniently presented for expert analysis.

[0064] In FIG. 3, a CPAP apparatus embodying the invention isillustrated. The CPAP unit comprises a motor 20 which drives a blower21. The speed of the motor 20 is controlled by an electronic speedcontrol unit 23. As an increase in motor speed also increases the blowerspeed which in turn increases the output air pressure of the blower 21,the speed control unit can be manipulated to vary the output pressure ofthe blower 21. The CPAP device also includes a snoring detection means22 wherein sounds are detected by a microphone 11. In its most generalform, the snoring detection means 22 is a pressure detection means andmicrophone 11 is a differential pressure sensor. The snoring detectionmeans 22 is conveniently in the form of the previously described device10. Electrical impulses are fed from said microphone 11 to anamplifier/filter/processor unit 26 which generates an electrical signalwhen snoring sounds occur. The motor speed control means is electricallyconnected to the snoring detection device 22 and increases the speed ofthe electric motor 20 by an analogue means in response to the electricalsignal generated by the snoring detection device. Accordingly, theoutput pressure of the CPAP unit increases in response to detection ofsnoring.

[0065] When a snore or sequence of snores is detected by the snoringdetection means 22 a signal is generated. The speed control unit 23increases the speed of the fan motor and the output pressure isincreased. As snoring is caused by vibration of the soft palate, it istherefore indicative of an unstable airway and, as previously described,is a warning signal of the imminence of upper airway occlusion inpatients that suffer obstructive sleep apnea. Snoring is itselfundesirable not only as it is a disturbance to others but it is stronglybelieved to be connected with hypertension. If the resultant increase inCPAP pressure is sufficient to completely stabilize the airway, snoringwill cease if a further snoring sound is detected, the CPAP pressure isincreased again. This process is repeated until the upper airway isstabilized and snoring ceases. Hence, the occurrence of obstructiveapnea can be eliminated by application of minimum appropriate pressureat the time of use.

[0066] In order to ensure that the CPAP pressure is maintained at alevel as low as practicable to prevent the onset of apnea, the preferredembodiment also includes a means to decrease the pressure if an extendedperiod of snore free breathing occurs. For example, this can be done byautomatically reducing the CPAP pressure at a gradual rate as long assnoring is not detected. The rate at which the CPAP pressure isdecreased in the absence of snoring is preferably much less than therate at which it is increased when snoring is detected. This can beachieved, for example, by the amplifier/filter/processor unit 26, in theabsence of an electronic signal from the microphone 11, continuouslygradually reducing the blower speed over a period of time but increasingthe blower speed in incremental steps each time a snore is detected bythe microphone 11.

[0067] In use, a patient may connect himself to the CPAP unit and go tosleep. The CPAP pressure is initially at a minimum operating value of,for example, approximately 3 cm H₂O gauge pressure so as not to causethe previously mentioned operational problems of higher initialpressures. Not until some time after going to sleep, and the patient'sbody relaxes, will the airway start to become unstable and the patientstart to snore. The detection apparatus 22 will then respond to a snore,or snore pattern, and via the processor 26 increase the motor speed suchthat CPAP pressure increases by 1 cm H₂O for each snore detected. TheCPAP pressure can be increased relatively rapidly, if the patient'scondition so requires, to a working pressure of the order of 8-10 cm,which is a typical requirement. An upper pressure limiting device can beincorporated for safety. Also, for ease of monitoring the variation overtime in patient conditions, a parameter such as pressure output can berecorded in some convenient retrievable form for periodic study by thephysician.

[0068] If for example in the early stages of sleep some lesser CPAPpressure will suffice, the CPAP unit of the present invention will notincrease the pressure until needed, that is, unless the airway becomesunstable and snoring recommences no increase is made to the airwaypressure.

[0069] By continuously decreasing the CPAP pressure at a rate of, forexample, 1 cm H₂O each 15 mins. in the absence of snoring the pressureis never substantially greater than that required to prevent apnea.However, when a snore or snoring pattern is detected, the decreasingCPAP pressure mode will be completely overwhelmed by a greater increase,about 1 cm H₂O per detected snore or snoring pattern. Once a stablesleeping pattern is achieved, the preferred embodiment will thencontinually test to ensure that the CPAP pressure is as low as ispracticable. Should the CPAP pressure be decreased to such n extent thatthe upper airway becomes unstable and snoring recommences, the pressureis reincreased to ensure that apnea is prevented, it being rememberedthat the snoring pattern is a precursor to apneic episodes.

[0070] The flexibility of the invention can be illustrated by thefollowing example.

[0071] It is known that a patient's maximum propensity to suffer sleepapnea occurs during REM sleep. An airway that was otherwise stable at agiven CPAP pressure may become unstable during REM sleep. Should thishappen snoring will set in before apnea occurs. In such circumstances,the present invention will raise the CPAP pressure in response to thesnoring, thus preventing the onset of apnea. The REM sleep passes, thepatient's airway becomes more stable and the higher airway pressure isno longer required. In such circumstances, the CPAP pressure will begradually reduced until the first sign of snoring reoccurs at whichpoint the pressure will again be increased.

[0072] A patient normally makes at least one loud snort or snoring soundat the end of an occurrence of apnea and the present invention willrespond to this unusually loud sound to increase the CPAP pressure. Thuseven if apnea should occur without the usual precursor of snoring, theairway pressure can still be adjusted upward in response to theabnormally loud breathing sounds generated at the end of the apneicperiod.

[0073] The present invention thus provides a CPAP device which modifiesthe CPAP pressure according to variations in a patient's requirementsthroughout an entire sleep period. It will be clear to those skilled inthe art that the present invention can cope with the variation in airwaypressure requirements such as may occur during a single sleep period, itwill also be able to cope with variations in CPAP pressure requirementsdue to a general improvement or deterioration in a patient's generalcondition as may take place over a longer period of time.

[0074]FIG. 4 illustrates in block form the circuitry of the CPAP deviceof FIG. 3. A snoring detection apparatus 22 is comprised of themicrophone 11 attached to the nose mask 12. The electrical signals ofthe microphone 11 are sent to a Filter/Amplifier/Processor 26 whichgenerates a control signal indicative of the recognition of a snoringpattern equivalent to a predetermined pattern.

[0075] Such control signals are sent to a feedback speed controller 23.The speed controller 23 comprises a ramp generator and voltage tofrequency converter 24 for control of a switch mode power supply (SMPS)15, which provides the power to run the motor 20 turning the blower 21.

[0076] The maximum output of the SMPS 15, and therefore the maximumpressure delivered to the mask 12, is limited by a pressure time control17.

[0077] In another aspect of the invention, shown in FIGS. 5 and 6, thereis provided a control circuit 33 comprising a delay control 25, a timer24, a switch mode power supply (SMPS) 15, and an upper pressure control17. In the timer 24 a square wave pulse train, is generated where theduty ratio can be varied by the delay control 25. This pulse train, inthe form of a current, is applied to a capacitor 19 to obtain a rampvoltage. Hence the output of the timer 24 and the input of the SMPS 15is a voltage increasing with respect to time. The output of the SMPS 15,and therefore the motor voltage and speed, follow the input.

[0078] The minimum blower speed is preset so as to give effectiveoperation of the air blower 21 and a minimum airway pressure which iscomfortable to the patient. Typically a minimum pressure of 3-5 cm H₂Owill have negligible effect on most patients.

[0079] The desired maximum airway pressure, being the intendedtherapeutic airway pressure, is set by adjusting the variable control17. The magnitude of this pressure will vary according to therequirements of the individual patient but will typically be in therange 10-20 cm H₂O.

[0080] When the delay control 25 is not set to zero minutes, theapparatus commences operation at the minimum motor speed and graduallyincreases the motor speed over a period of time selected before reachingthe maximum preselected speed according to the previous adjustment ofcontrol 17. When the delay control 25 is set to zero minutes airwaypressure comes up to the full level as set by adjustment 17 in a shortperiod of time.

[0081] By this arrangement sleep is commenced with a low and comfortableair pressure but then automatically increased after a selectable periodof time to the desired therapeutic pressures so as to provide anadequate pneumatic splint to the airway passages during the latterstages of sleep when apnea is likely.

[0082] A convenient way to gauge whether a correct therapeutic, ormaximum, pressure has been selected is to use the diagnostic device 10of this invention while the patient is undergoing CPAP therapy. Shouldthe recorded data show no signs of apneic periods then the setting maybe assumed to be adequate at least for the patient when in a similarphysical condition. Another long term benefit can be gained by recordingthe pressure level applied to the patient during sleep periods in whichCPAP is applied using the feedback device of this invention. By makingsuch recordings spaced over a period of time the skilled physician candiagnose any long term changes in the patient's condition.

[0083]FIG. 7 illustrates a pressure detection device comprising apressure sensor, in pressure communication with the container of a nosemask. Air, being inhaled by the patient, enters the nasal passagewaysthrough the opening in the nose mask and is exhaled in the reversedirection. The pressure sensor is ideally located to detect bothpressure waves generated by the patient snoring or by variations in therespiration rate or pattern of the patient. Hence the snoring sounds andbreathing variations are captured and concentrated by this arrangement.Alternatively, the pressure sensor may be located within or attachedexternally to a nasal prong device.

[0084] The detection device can be used in a diagnostic device or afeedback control. In the case of the detection device being used indiagnostic equipment there is connected to the pressure sensor acomputing system as shown in FIG. 12 which analyses and records signalsfrom the pressure sensor in a data store. These signals can be stored ona real time basis or after further processing in the form of indexessuch as the number of apneic episodes, the number of hypopneas, theirduration, etc. The recorded data can then be reviewed by a physician fordiagnosis.

[0085]FIG. 9 shows the sources of pressure waves detected by thepressure sensor. The high frequency wind noise is generated by the airblower and is extraneous for the purposes of interpreting the conditionof the patient. Pressure waves at a frequency of 30 to 50 Hz areindicative of snoring and could be detected by using a particularembodiment of the pressure sensor in the form of a microphone.Disturbances in breathing pattern are detected at a very low frequencyrelating to breathing rate of approximately 0.5 Hz. The output of thesensor is a composite of the pressure waves generated by all thesesources.

[0086]FIG. 10 shows a schematic electronic circuit which first amplifiesthe output of the pressure sensor before passing it through a series offilters to separate the pressure waves at the frequencies of interest.The high frequency wind noise is eliminated and signals indicative ofsnoring and breathing are obtained. The breathing signal is furtherprocessed to give information on breathing rate, flow rate and volumeper breath.

[0087]FIG. 2a shows a graph representing sound amplitudes obtained fromthe snoring signal filtered from the pressure detection device. Themajor calibration in the time scale direction represents two minutes.

[0088] The effect of blower motor noise can be diminished or completelyremoved by setting a low gain on the recording device or passing thesignal through an amplitude filter to effectively ignore all soundsbelow a particular minimum amplitude or by passing the signals through alow pass frequency filter to effectively ignore sounds above its cutofffrequency. An alternative method is to use a sound attenuator in the airline proximate the blower.

[0089] Part A of FIG. 2a is indicative of normal breathing, part Bindicates soft to moderate snoring, part C shows constant loud snoringand part E shows periods of silence punctuated by snoring. In section Dof the chart of FIG. 2a, it can be seen that the breathing soundintensity rises and falls. This is indicative of obstructive hypopnea, acondition in which the breath-by-breath intensity decreasesprogressively, and then increases. In this pattern the decreasingintensity of the snoring occurs when the upper airway is almost, but notentirely, sucked closed by strong inspiratory efforts. This pattern is a“pre-apneic” pattern.

[0090] The following part E is therefore quickly interpreted by askilled physician as being indicative of sleep apnea, with periods ofairway occlusion which terminate with one or more loud breathing soundsfollowed by further occlusions.

[0091] The correlation between snoring patterns and arterial oxygen isshown in FIG. 2b. Clearly the snoring patterns are an accurate parameterfor detecting imminent apneic episodes, and more importantly periods oflow oxygen supply to the brain and other organs.

[0092]FIG. 8 shows the volume of air inhaled (or exhaled) by the patientwith each breath as determined by the volume integrator from thebreathing signal filtered from the pressure sensor. Part A of FIG. 8shows normal breathing, while Part B shows shallow breathing orhypoventilation. A decreasing pattern of air volume inspired by thepatient can be indicative of the imminent onset of apnea or can beundesirable as the patient's arterial oxygen level falls below anacceptable level.

[0093]FIG. 10 shows how the processing system can be set up to respondwhen the average volume of a predefined number of the most recentbreaths falls below the volume of a predefined long term average volumefor that patient.

[0094]FIG. 11 shows how the computing system can accept and analyze anyor all of the processed signals from the pressure sensor and using thesignal, alone or by comparison with control data for that patient,control the speed of the blower to vary the pressure of the airdelivered to the patient's nose mask.

[0095]FIG. 13 shows an example of how the signal indicative of snoringalone is received by the computing system and the computing systemincreases pressure in accordance with predefined procedure.

[0096] Thus, the recorded information derived from the signal of thepressure sensor can be used for diagnostic purposes, such as initialdiagnosis of sleep apnea or hypopnea, without the need for the patientto stay overnight in an observation facility, the sound and breathingpatterns can be analyzed by a programmed microprocessor or computingsystem as shown in FIG. 12 so as to record tables of indexes such asnumber of hypopneas and/or apneic episodes, their duration and time ofoccurrence. This is of economic significance because the cost of oneovernight observation is comparable to the purchase price of a CPAPdevice.

[0097] Furthermore, diagnostic apparatus in accordance with the presentinvention is suited for use by a patient with minimal supervision andtherefore may be used successfully at home, the recorded diagnosticinformation being conveniently presented for expert analysis.

[0098] In FIG. 3, a CPAP apparatus embodying the invention isillustrated. The CPAP unit comprises a motor 20 which drives a blower21. The speed of the motor 20 is controlled by an electronic speedcontrol unit 23. As an increase in motor speed also increases blowerspeed which in turn increases the output air pressure of blower 21, thespeed control unit can be manipulated to vary the output pressure of theblower 21. The CPAP device also includes a pressure detection means 22wherein pressure waves in the form of electrical signals are detected bya pressure sensor 11. The pressure detection means 22 is conveniently inthe form of the previously described device illustrated in FIG. 7.Electrical signals are fed from said sensor 11 to anamplifier/filter/processor unit 26 which may be inside or outside theblower unit casing and generates an electrical signal when snoring soundand/or deviations of breathing parameters from predetermined valuesoccur. The motor speed control means is electrically connected to thepressure detection device 22 while being electrically isolated from thepatient and increases the speed of the electric motor 20 by an analoguemeans in response to the electrical signal generated by the pressuredetection device. Accordingly, the output, pressure of the CPAP unitincreases in response to detection of snoring and/or deviations ofbreathing parameters from predetermined values.

[0099] The method of operation can be illustrated by considering theeffect of a snore or sequence of snores detected by the pressure sensoras shown in FIG. 13. When a snore or sequence of snores is detected bythe snoring detection means 22 a signal is generated. The speed controlunit 23 increases the speed of the fan motor and the output pressure isincreased. As snoring is caused by vibration of the soft palate, it istherefore indicative of an unstable airway and, as previously described,is a warning signal of the imminence of upper airway occlusion inpatients that suffer obstructive sleep apnea. Snoring is itselfundesirable not only as it is a disturbance to others but it is stronglybelieved to be connected with hypertension. If the resultant increase inCPAP pressure is sufficient to completely stabilize the airway, snoringwill cease. If a further snoring sound is detected, the CPAP pressure isincreased again. This process is repeated until the upper airway isstabilized and snoring ceases. Hence, the occurrence of obstructiveapnea can be eliminated by application of a minimum appropriate pressureat the time of use.

[0100] In order to ensure that the CPAP pressure is maintained at alevel as low as practicable to prevent the onset of apnea, the preferredembodiment also includes a means to decrease the pressure if an extendedperiod of snore free breathing occurs. For example, this can be done byautomatically reducing the CPAP pressure at a gradual rate as long assnoring is not detected. The rate at which the CPAP pressure isdecreased in the absence of snoring is preferable much less than therate at which it is increased when snoring is detected. This can beachieved, for example, by the amplifier/filler/processor unit 26, theabsence of an electronic signal from the pressure sensor 11,continuously gradually reducing the blower speed over a period of timebut increasing the blower speed in incremental steps each time a snoreis detected by the pressure sensor 11.

[0101] A predetermined deviation of any or all of the breathingparameters, flow rate, volume or breathing rate from a predeterminedcommon value can generate a signal in a similar way. Hence a fall in thevolume of air inspired or expired per breath below a preset value cangenerate a signal which increases the speed of the fan motor andincreases the output pressure. After the breathing volume has returnedto the control setting for a predetermined period, the fan motor speedwill be decreased slowly until a snore or unacceptable breathing patternis again detected by the pressure sensor.

[0102] In use a patient may connect himself to the CPAP unit and go tosleep. Only one connection is required apart from the normal CPAPcircuit and this is simply the connection from the pressure sensor tothe amplifier/filter/processor unit. No electrodes or other sensors haveto be attached to the patient's body as the pressure sensor isconveniently located in the CPAP mask. The CPAP pressure is initially ata minimum comfortable operating value of, for example, approximately 3cm H₂O gauge pressure so the as not to cause the previously mentionedoperational problems of higher initial pressures. Not until some timeafter going to sleep, and the patient's body relaxes, will the airwaystart to become unstable and the patient start to snore or exhibitabnormal breathing patterns. The detection apparatus 22 will a respondto the snore, or snore pattern or abnormal breathing pattern and via theprocessor 26 increase the motor speed such that CPAP pressure increasesby 1 cm H₂O for each snore or predetermined abnormality in breathingpattern detected. The CPAP pressure can be increased relatively rapidly,if the patient's condition so requires, to a working pressure of theorder of 8-10 cm H₂O, which is a typical requirement. An upper pressurelimiting device can be incorporated for safety. Also, for ease ofmonitoring the variation over time in patient conditions, a parametersuch as pressure output can be recorded in some convenient retrievableform for periodic study by the physician.

[0103] If for example in the early stages of sleep some lesser CPAPpressure will suffice, the CPAP unit of the present invention will notincrease the pressure until needed, that is, unless the airway becomesunstable and snoring or abnormal breathing patterns recommence, noincrease is made to the airway pressure.

[0104] By continuously decreasing the CPAP pressure as a rule of, forexample, 1 cm H₂O each 15 mins in the absence of snoring or abnormalbreathing patterns, the pressure is never substantially greater thanthat required to prevent apnea or other undesirable respiratoryconditions. However, when a snore, or snoring patterns or abnormalbreathing pattern, is detected the decreasing CPAP pressure mode will becompletely overwhelmed by a greater increase, about 1 cm H₂O perpredetected snore or snoring pattern or predetermined abnormality inbreathing pattern. Once a stable sleeping pattern is achieved, thepreferred embodiment will a continually test to ensure that the CPAPpressure is as low as is practicable. Should the CPAP pressure bedecreased to such an extent that the upper airway becomes unstable andsnoring or unacceptable breathing patterns recommence, the pressure isreincreased to ensure that apnea is prevented, it being remembered thatthe snoring or abnormal breathing pattern is a precursor to apneicepisodes or other undesirable respiratory conditions such as shallowbreathing or hypopnea.

[0105] The flexibility of the invention can be illustrated by thefollowing example.

[0106] It is known that a patient's maximum propensity to suffer sleepapnea occurs during REM sleep. An airway that was otherwise stable at agiven CPAP pressure may become unstable during REM sleep. Should thishappen snoring and/or particular deviations in breathing patterns willset in before apnea occurs. In such circumstances, the present inventionwill raise the CPAP pressure in response to the snoring or deviation inbreathing patterns, thus preventing the onset of apnea or otherundesirable respiratory condition. After the REM sleep passes, thepatient's airway becomes more stable and the higher airway pressure isno longer required. In such circumstances, the CPAP pressure will begradually reduced until the first sign of snoring and/or unacceptablebreathing patterns reoccurs at which point the pressure will again beincreased.

[0107] A patient normally makes at least one loud snort or snoring soundat the and of an occurrence of apnea and the present invention willrespond to this unusually loud sound to increase the CPAP pressure. Thuseven if apnea should occur without the usual precursor of snoring orabnormal breathing pattern, the airway pressure can still be adjustedupward in response to the abnormally loud breathing sounds generated atthe end of the apneic period.

[0108] The present invention thus provides a CPAP device which modifiesthe CPAP pressure according to variations in a patient's requirementsthroughout an entire sleep period. It will be clear to those skilled inthe art that the present invention can cope with the variation in airwaypressure requirements such as may occur during a single sleep period, itwill also be able to cope with variations in CPAP pressure requirementsdue to a general improvement or deterioration in a patient's generalcondition as may take place over a longer period of time.

[0109]FIG. 12 illustrates in block form the circuitry of the feedbacksystem. A pressure detection apparatus is provided either integral withor attached to the CPAP mask worn by the patient. The electrical signalsfrom the pressure transducer are amplified and filtered to providepressure waves of the desired frequencies indicative of snoring andbreathing. The pressure wave indicative of breathing is furtherprocessed to generate signals indicative of flow rate, volume andbreathing rate. Any or all signals are fed to a computing system whichanalyses the signals for deviation from predetermined values orpatterns. The computing system may itself calculate control values ofpatterns for each patient based on moving average values or such valuesor patterns will be preprogrammed into the computing system.

[0110] Where signals deviate from predetermined values or patterns thecomputer system generates a signal which is sent to the feedback speedcontroller on the blower motor. Increasing blower speed increases theair pressure and level of CPAP treatment delivered to the patient. Thespeed and pressure are increased until signals detected from the patientare within the acceptable range of control values or patterns and thespeed and pressure are maintained at that level.

[0111] The maximum output of the blower can be limited by limiting thesignal from the computer to correspond to a predetermined motor speed.

[0112] A convenient way to gauge whether a correct therapeutic ormaximum, pressure has been selected is to use the diagnostic deviceshown in FIG. 7 of this invention while the patient is undergoing CPAPtherapy. Should the recorded data show no signs of apneic periods thenthe setting may be assumed to be adequate at least for the patient whenin a similar physical condition. Another long term benefit can be gainedby recording the pressure level applied to the patient during sleepperiods in which CPAP is applied using the feedback device of thisinvention. By making such recordings spaced over a period of time theskilled physician can diagnose any long term changes in the patient'scondition.

[0113] It is to be understood that while the invention has beendescribed above in conjunction with preferred specific embodiments, thedescription and examples are intended to illustrate and not limit thescope of the invention, which is defined by the scope of the appendedclaims.

1. A method of CPAP therapy comprising the steps of providing releasablesealed air communication with a patient's respiratory system from an airpressure source, and delivering pressurized air from said source to thepatient so that the air pressure automatically gradually increases overa period of time to reach a predetermined maximum therapeutic operatinglevel, wherein said period of time exceeds a single breathing cycle ofthe patient.
 2. The method of claim 1 wherein the time period of theautomatic increase can be adjusted.
 3. A method of CPAP therapycomprising the steps of providing releasable sealed air communicationwith a patient's respiratory system from an air pressure source, anddelivering pressurized air from said source as the patient attempts tofall asleep while automatically gradually increasing said pressurizedair over a period of time to reach a predetermined maximum therapeuticoperating level, wherein said period of time exceeds a single breathingcycle of the patient.
 4. The method of claim 3 wherein the time periodof said automatic increase can be adjusted.
 5. A method of CPAP therapycomprising the steps of providing releasable sealed air communicationwith a patient's respiratory system from an air pressure source, anddelivering pressurized air from said source to the patient so that theair pressure automatically gradually increases over a period of time toreach a predetermined therapeutic operating level, wherein said periodof time exceeds a single breathing cycle of the patient.
 6. The methodof claim 5 wherein the time period of the automatic increase can beadjusted.
 7. A method of CPAP therapy comprising the steps of providingreleasable sealed air communication with a patient's respiratory systemfrom an air pressure source, and delivering pressurized air from saidsource as the patient attempts to fall asleep while automaticallygradually increasing said pressurized air over a period of time to reacha predetermined therapeutic operating level, wherein said period of timeexceeds a single breathing cycle of the patient.
 8. The method of claim7 wherein the time period of said automatic increase can be adjusted. 9.An air flow device, useful in CPAP therapy of a patient, comprising:means for delivering variable pressure levels of pressurized air to apatient's respiratory system; means for controlling the period of timeduring which continuously delivered pressurized air automaticallygradually increases to a predetermined therapeutic operating level,wherein said period of time exceeds a single breathing cycle of thepatient; and, means for automatically maintaining the deliveredpressurized air at the operating therapeutic level after the operatingtherapeutic level has been reached.
 10. An air flow device, useful inCPAP therapy of a patient, comprising: a motor with a blower; a speedcontrol unit coupled to said motor; and a control circuit coupled tosaid speed control, wherein said control circuit causes said blower toautomatically gradually increase to a predetermined therapeuticoperating level wherein said increase occurs over a period of timeexceeding a single breathing cycle of a patient.
 11. The device of claim10 wherein said control circuit may be set to adjust the time period ofthe automatic increase.
 12. The device of claim 11 wherein said controlcircuit may be set to adjust the therapeutic operating level.
 13. Thedevice of claim 12 wherein said control circuit commences operation at aminimum pressure.
 14. The device of claim 13 wherein said controlcircuit comprises: a delay control; a timer, a switch mode power supply,and an upper pressure control.